Two American aid workers who contracted Ebola while working in West Africa have been released from the hospital. Doctors say the former patients are no longer contagious, posing no threat to others.

Kent Brantly, a physician with the humanitarian group Samaritan's Purse, was discharged from Atlanta's Emory University Hospital on Thursday. Missionary Nancy Writebol, of SIM USA, was discharged Tuesday.

"God saved my life," said a gaunt Brantly, whose arrival at a news conference Thursday drew applause from the crowd. He thanked his medical team and the millions of people around the world praying for his recovery. "Please do not stop praying for the people of West Africa."

Bruce Ribner, medical director of the hospital's infectious disease unit, said Brantly will go to an undisclosed location with his wife and children.

Brantly and Writebol were flown to Emory from West Africa in early August and were treated in the hospital's specialized unit.

Ribner said the hospital performed extensive blood and urine tests on both patients and consulted with the Centers for Disease Control and Prevention before deciding the two missionaries were ready to be released. Both are now likely immune to the strain of Ebola with which they were infected. There are four other known strains.

Five doctors and 21 nurses cared for Brantly, 33, and Writebol, 59, during their stay.

"After a rigorous course of treatment and testing, the Emory health care team has determined that both patients have recovered from the Ebola virus and can return to their families and community without concern for spreading this infection to others," Ribner said. "We are profoundly grateful for the opportunity to have applied our training, our care and our experience to meet their needs. All of us who have worked with them have been impressed by their courage and determination."

In his statement, Brantly said his family arrived in Liberia last November, and he saw his first Ebola patient in June. "We took every precaution to protect ourselves from this dreaded disease," Brantly said.

On July 23, a few days after sending his family home for safety, Brantly said he woke up feeling sick. He soon learned he was infected.

The World Health Organization says 1,350 people have died from Ebola during the outbreak, more than all earlier outbreaks combined.

Writebol chose not to appear publicly. Brantly said that as she left her isolation unit, she said, "To God be the glory."

In a written statement, Writebol's husband, David, said, "Nancy joined the ranks of a small but hopefully growing number of survivors. ... Nancy is free of the virus, but the lingering effects of the battle have left her in a significantly weakened condition. Thus, we decided it would be best to leave the hospital privately to be able to give her the rest and recuperation she needs at this time. During the course of her fight, Nancy recalled the dark hours of fear and loneliness but also a sense of the deep, abiding peace and presence of God, giving her comfort."

Ribner said he hopes what he and his colleagues learned about treating Ebola can help save patients in Africa.

While in Liberia, Brantly received a blood transfusion from an Ebola survivor.

Brantly and Writebol received doses of an experimental drug called ZMapp, which includes man-made antibodies against Ebola. Although ZMapp has shown promise in animals, it has not been tested in humans. It's not known whether ZMapp cured their disease, although getting good supportive care at Emory, one of the world's best hospitals, probably improved their chances of survival.

"If the question is, 'Did ZMapp do this?' The answer is that we just don't know," says Anthony Fauci, director of the National Institute of Allergy and Infectious Disease. "People who are in much less sophisticated medical care conditions in West Africa are recovering 50% of the time."

Without a carefully designed trial — involving a comparison group that doesn't receive the drug — doctors can't make conclusions about how a treatment works. About half the Ebola patients in the outbreak are surviving without the experimental drug. A Spanish priest who received ZMapp died, Fauci said.

Three Liberian health workers — two doctors and a nurse — also received ZMapp. According to the World Health Organization, the nurse and one of the doctors "show a marked improvement, while the condition of the second doctor is serious but has improved somewhat.

The drug's manufacturer, Mapp Biopharmaceutical of San Diego, has said there is no more of the drug left.

According to CNN, two blood tests done over a two-day period had to come back negative for Ebola before Brantly could be discharged. David Writebol was released from quarantine this week. Doctors had observed him for three weeks, monitoring him for signs of fever. Ebola can have an incubation period of up to 21 days.

People generally aren't considered contagious unless they have symptoms of Ebola, such as fever.

The CDC has sent at least 50 staffers to West Africa to help contain the epidemic.

"We must recommit to doing all we can to increase their chances of survival and to stop the spread of Ebola," CDC Director Thomas Frieden said in a statement. "This outbreak is unprecedented, and it's likely to get worse before it gets better. We must respond in unprecedented ways to stop the outbreak as soon as possible."

In concluding his statement, Brantly said he is "glad for any attention my sickness has attracted to the plight of West Africa in the midst of this epidemic. Please continue to pray for Liberia and the people of West Africa, and encourage those in positions of leadership and influence to do everything possible to bring this Ebola outbreak to an end."

Samaritan's Purse, the Christian humanitarian organization for which Brantly works, released this statement from its president, Franklin Graham, Thursday morning:

"Today, I join all of our Samaritan's Purse team around the world in giving thanks to God as we celebrate Dr. Kent Brantly's recovery from Ebola and release from the hospital. Over the past few weeks, I have marveled at Dr. Brantly's courageous spirit as he has fought this horrible virus with the help of the highly competent and caring staff at Emory University Hospital. His faithfulness to God and compassion for the people of Africa have been an example to us all.

"I know that Dr. Brantly and his wonderful family would ask that you please remember and pray for those in Africa battling, treating and suffering from Ebola. Those who have given up the comforts of home to serve the suffering and the less fortunate are in many ways just beginning this battle.

"We have more than 350 staff in Liberia, and others will soon be joining them, so please pray for those who have served with Dr. Brantly — along with the other doctors, aid workers and organizations that are at this very moment desperately trying to stop Ebola from taking any more lives."